Since the vigorous development of electronic technology, the electronic product has been widely used, and therefore, the problem of the power supply used by the electronic product becomes a very important issue. Currently, the electronic product generally uses a switching type power supplying manner to realize supplying the power, and the switching type may perform a switching operation of the switch through the pulse width modulation (PWM) technique or the pulse frequency modulation (PFM) technique.
Because a grayscale image in the liquid crystal display has 256 grayscale values, the grayscale value is a concept of the brightness. A range of the color shade is 0 to 255, where 0 is black and 255 is white. When a variation of the grayscale value of the electronic product is larger, the load of the liquid crystal display is also larger. Otherwise, the load of the liquid crystal display is also smaller. Usually, when the electronic product works under a large load condition, it uses the pulse width modulation (PWM) technique to control the switching action of the switch; at this time, the pulse width modulation (PWM) technique has good efficiency and better control performance, and the working loss thereof has a transmitting loss and a switching loss. When the electronic product is at a light load, if it still uses the pulse width modulation (PWM) technique to control the switching action of the switch, at this time, the transmitting loss may be decreased due to the electronic product at the light load; however, since a switching frequency is fixed, the switching loss does not decrease as the load decreases. Therefore, when the electronic product is at the light load, it still uses the working mode of the pulse width modulation (PWM), such that the whole loss is large, the efficiency is decreased, and it is not conducive to energy-saving design.
Usually, when the electronic product works under a light load condition, it generally uses the pulse frequency modulation (PFM) technique to control a switching action of a switch. Namely, when the load is decreased, a switch frequency of the switch is also decreased, thereby decreasing the switching loss of the switch and maintaining the higher working efficiency.
Therefore, the electronic product may automatically select the pulse width modulation (PWM) technique or the pulse frequency modulation (PFM) technique to turn on or turn off the switching mode according to the load state, which is the trend of the electronic development.